586 PRACTICE OF AGRICULTURE. Part III. 



intervening material between the metals and the earth, even if it were a bog, " provided 

 it admitted a man to walk over it." (Examination, ^c. 1819.) The Somersetshire 

 morass is so extremely soft, he says, " that when you ride in a carriage along the road, 

 you see the water tremble in the ditches on each side ; and after there has been a slight 

 frost, the vibration of the water from the carriage on the road will be so great as to break 

 the young ice. I never use large stones on the bottom of a road ; I would not put a 

 large stone in any part ,of it, nor faggots, nor any material larger than will weigh six 

 ounces. If a road be made smooth and solid, it will be one mass, and the effect of the 

 substratum, whether clay or sand, can never be felt in effect by carriages going over the 

 road ; because a road well made unites itself in a body like a piece of timber or a board." 



3632. An instructive proof of the preference given by M'Adam to a soft base is derived 

 from a case which occuiTed near Montrose. This case was sent to him by Paterson in 

 the following report : " This road," says the reporter, " for about a mile, goes over a bank 

 of sea-beach, many feet in depth, and all round stones from two to five or six inches in 

 diameter. Always as the stones above three inches work up, and make their appearance 

 on the surface, they are taken off to the side of the road, and broken to the ordinary size. 

 This has been done several times every year for many years back, but the road always 

 continues loose and open as ever." The answer of M'Adam was, " The road you have 

 sent me a report of is novel in its situation, but very far from hopeless. The sea-beach, 

 of which it is wholly composed, should be picked ; that is to say, the large-sized pebbles 

 should be carefully removed from the surface, and carried to the side of the road, and 

 there broken, not to what your surveyor calls my size, which is six ounces, but smaller, 

 say to three or four ounces. And / must also warn you, that any round stone, when 

 broken in half so as to form a hemisphere, is nearly as unmanageable, and as little likely 

 to consolidate in a road, as one left quite round ; therefore, with regard to weight, your 

 stones must be taken so as to form as many angles as possible. No large pebble must 

 be left in sight upon the bottom of the road, otherwise they will work up through the 

 broken stones of which your road will be composed ; but having prepared a surface upon 

 which to place your road, by removing the large-sized pebbles (I mean all above six 

 ounces^ and evenly covering the surface with sand soil or other soft matter, lay on your 

 properly broken stones." Paterson entirely concurs with M'Adam in regard to the ad- 

 vantage of a soft base, adding, in his last publication {Letters, ^c 1822.), " although the 

 ground under the materials can never be too dry, the materials never unite so firmly when 

 placed upon a hard rock or upon gravel, as they do upon earth, moss, or sand. There 

 should always, therefore, be a few inches of the one or the other of these put under the 

 road, as a bed for the materials, where it is on a rocky or gravelly bottom." 



3633. When the basis consists partly of firm, and partly of loose, materials, or moved 

 earth, some nicety is required to determine the allowance for the sinking of the latter ; and, 

 indeed, roads, under such circumstances, cannot often be finished out of hand. Some 

 judicious directions on this subject are given by Paterson. " When a road," he observes, 

 " is formed along the side of a hill or sloping bank, the earth that is produced from the 

 side-cutting makes up a part of the breadth of the road ; so that the road is formed, partly 

 on the solid ground, and partly on the embankment. All new-made-up earths or em- 

 bankments subside a little, whatever be the nature or quality of the stuff of which they 

 are composed : for which reason, that part of the breadth of the road, that is formed upon 

 the embankment, should be raised a little higher than the solid ground. No precise rule 

 can be given to ascertain exactly how much the different kinds of earths, clays, gravel, 

 &c. will subside ; but the following has been found so near to the truth, in most cases, 

 that it may with safety be admitted as a general rule. At all places where there are em- 

 bankments, whether over hollow ground, or along the side of a sloping bank, for every 

 foot that these embankments or mounds are raised in height, one inch may be allowed for 

 subsiding. So that if an embankment, or the outer edge of a road formed from the side- 

 cutting, requires, for instance, six feet deep of forced earth to bring it to the level required, 

 in that case it should be made six inches higher ; namely, six feet six inches upon the 

 newly made up ground ; and it will be found, in general, to be about six months, from 

 the time that the embankment has been made, until it has become properly consolidated." 



3634. Where the bottom is naturally wet and spongy, Stevenson observes, it is well to 

 ram it with chips of stone, or with rubbish somewhat freed from earthy particles. It is 

 extremely desirable, in every situation, that the road-metal should be broken to a uniform 

 size, so as to form a compact body throughout. But, as the preparation of the small 

 metal suitable for the surface of a road is expensive, it will, in many situations, be found 

 advisable to lay a stratum or course of hand-laid stones, of from five to seven inches 

 in depth, with their broadest ends placed downwards, and the whole built compactly 

 together, upon the prepared bed or soil. 



3635. The materials of the road may be considered in regard to their nature or kind, 

 the proper size and weight, the outline of their upper surface, and the mode of laymg 

 them on and consolidating them. 



